Kevin Plaxco, a biochemist at the University of California, Santa Barbara, has developed a prototype of a DNA-based cocaine detector that could lead the way to a "breathalyzer" style portable detector for cocaine.
So far the device has sniffed out cocaine mixed with many of the substances drug dealers use to cut the drug, including flour, sugar, baking soda, coffee, and mustard powder. It also sees through such chemical masking agents as cobaltous thiocyanate, which sophisticated drug dealers mix into cocaine to fool the Scott test. The detector works by passing an electronic signal through a type of DNA molecule, called an aptamer, that binds with other specific molecules, in this case cocaine.
This particular type of aptamer, which is synthetic, is usually floppy. When it binds with cocaine, however, it stiffens up and assumes a structured, folded shape, which causes it to allow electrons to pass through it more readily.
Link (thanks, A. Fischer!)